An important element in the quality of silver halide emulsions is the size of the particles. It is highly desirable to have the capability of monitoring the size of the particles during the emulsion precipitation process, particularly during the early stage (nucleation) which largely dictates the end result.
In most cases the diameters of the nuclei are less than 0.1 micrometer. Methods suitable for measuring particle sizes in this size range can be found in the literature; small angle x-ray scattering, sedimentation field flow fractionation, proton correlation spectroscopy, ultracentrifugation, angular light scattering, turbidimetry, and size exclusion chromatography. Of the methods listed, turbidimetry is the most promising for on-line measuring purposes. However, it suffers interference from air bubbles which are inherent in agitated emulsion reactors. A second drawback is that the measurement from this method is in principle biased towards large particles in a population, giving high results rather than average results. This situation gets worse with wider particle size disparity.
The present invention overcomes the problems of the previous methods with a device that is easily manufactured. The apparatus of the present invention is a probe that measures the particle size of silver halide emulsions based on their relationship with solubility.